Method and apparatus for enhanced flameholding in augmentors

ABSTRACT

Techniques for the enhancement of the stability of an afterburning flame in the viscinity of a low pressure loss augmentor are provided by various geometrical modifications of the base region of the augmentor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Patent Application 61/236,456 filed Aug, 24, 2009, which is incorporated herein by reference.

STATEMENT OF GOVERNMENT SPONSORED SUPPORT

This invention was made with Government support under contract FA9550-08-C-0039 awarded by U.S. Air Force. The Government has certain rights in this invention.

FIELD OF THE INVENTION

The invention relates to thrust augmentors used in jet engines. In particular, the invention relates to techniques to enhance flameholding in augmentors.

BACKGROUND OF THE INVENTION

Thrust augmentors are used in jet engines as a means to provide additional thrust capability with little mechanical complexity. While the V-gutter has been used in the past, an alternate generic design for the flameholder uses a more streamlined shaped body for reducing the stagnation pressure loss and it includes a bluffbody with a rounded (or elliptic) nose, some streamwise length and a rectangular trailing edge. Fuel is injected through a set of ports upstream of the trailing edge, mixes with the hot gases and eventually forms a flame which is anchored by the recirculation downstream of the trailing edge. The present invention advances the art by disclosing new designs and methods for flameholding in augmentors.

SUMMARY OF THE INVENTION

In one aspect, the enhancement of afterburning flame stability and the change of the flow field in the wake region of new, low pressure loss flame augmentors, of variously modified base geometries, are disclosed in a high temperature (˜ 1300 K) vitiated flow. Flame liftoff height measurements are characterized by CH chemiluminescence, while the three-dimensional flow field is determined using stereo particle image velocimetry (PIV). The basic geometry of the augmentor is a rectangular body with a rounded nose. In one aspect, we find that a combination of both 2-D and 3-D geometric changes provides the best flameholding, i.e. the highest flame stability (lowest liftoff height), and furthermore, when local cavities are in phase with the fuel jets, the performance is optimal. Furthermore, it is conjectured from the PIV experiments that the observed stability enhancement is attributed to multi-dimensional vortices induced by both the presence of the local cavity as well as the two-dimensional geometric change.

DETAILED DESCRIPTION

Descriptions and figures of various embodiments of the present invention are disclosed in the following appendices:

Appendix A: A paper (10 pages) entitled “A Method and Apparatus for Improved Flameholding in Augmentors” by Kim et al.

Appendix B: A paper (4 pages) entitled “Stereo PIV Measurements of a Geometrically Modified Flame Augmentor Base” by Kim et al.

Appendix C: A paper (33 pages) entitled “Flame Liftoff Height Dependence on a Geometrically Modified Bluff Bodies in a Vitiated Flow” by Kim et al.

Appendix D: A paper (27 pages) entitled “The improvement of blowout limit in partially/fully premixed flames with geometrically modified bluffbody bases” by Kim et al.

As one of ordinary skill in the art will appreciate, various changes, substitutions, and alterations could be made or otherwise implemented without departing from the principles of the present invention. Accordingly, the examples and drawings disclosed herein including the appendix are for purposes of illustrating the preferred embodiments of the present invention and are not to be construed as limiting the invention. 

1. A flame augmentor for use in a jet engine, wherein the bluffbody base of said flame augmentor comprises a plurality of two-dimensional and three-dimensional geometrical features to enhance flameholding. 